Kepler, a prolific hunter for other Earths, is suddenly in trouble (+video)

Kepler was launched in March 2009 as a kind of planetary census taker. The mission's aim is to observe the same 170,000 stars in a hunt for rocky planets orbiting in their stars' habitable zones – roughly defined as a distance that leaves a planet's surface not too hot or not too cold, but just right for liquid water to persist on its surface. Liquid water is a key prerequisite for organic life.

To date, Kepler has found Earth-mass planets. And it has found larger, super-Earths orbiting in their star's habitable zones. The Kepler team has yet to uncover its ultimate planets. But after bagging more than 2,700 planet-candidates so far, finding the first "just right" extra-solar planet isn't far off, says William Borucki, the mission's lead scientist.

"I'm absolutely delighted that we've got all this data," he said at the briefing. "The mission was designed for four years. It operated four years. It gave us excellent data for four years. On the other hand, I would have been even happier if it continues another four years."

The discoveries the additional data would have yielded "would have been in some sense frosting on the cake," he acknowledged. "But we have an excellent cake."

If Kepler can't be revived, analyzing the 2,700 planet-candidates in the queue so far will keep the team busy for at least two more years, he noted.

But engineers have some tricks up their sleeves they want to try before they give up and NASA declares the mission finished.

Reaction wheels spin constantly at high rates of speed, so engineers anticipate that they will fail at some point.

One approach would be to command the balky wheel to rotate back and forth to see if whatever is preventing it from operating can be dislodged. If the reaction wheel can't be revived, the team could try to reactivate the wheel they took out of service last year.

If that doesn't work, the team will examine other science missions the craft might be able to perform that don't require the level of precision pointing that planet-hunting does. That means relying on the thrusters more frequently to orient the craft, so remaining fuel supplies become a limiting factor.